High-pressure dry steam system and method of controlling the same



Feb. 6, 1968 E. L. PLAGMAN, JR HIGH-PRESSURE DRY STEAM SYSTEM AND METHODOF CONTROLLING THE SAME Filed May 10, 1966 9Jl l Unite This inventionrelates to a high-pressure dry steam system and to a method ofcontrolling the discharge of condensate for the system so that the rateof condensation and discharge thereof from the system are maintained inbalance with the high pressure dry steam output of the steam generator.

This invention relates particularly to a high pressure dry steam systememploying a steam generator having a predetermined rated output ofcombined pressure and dry steam and connected to a plurality of highpressure dry steam consuming devices having a total actual capacitywhich does not exceed the rated capacity of the generator. The generatormay comprise one or more separate units connected to a common header orto a main steam line.

More specifically, the invention relates to the method and means forrestricting the rate of discharge of accumulated condensate from eachdevice after a down period so that the rate of discharge of the totalcondensate, including both that accumulated and that currently beingproduced, in the entire system is maintained within limits such thatcondensate formation does not exceed the output capacity of the steamgenerator, thereby preventing carryover of wet steam and water from thegenerator into the system, and so that, after the system is brought upto operating pressure and temperature each device is maintained at itsrated capacity.

Though the present invention is directed particularly to the highpressure dry steam systems, it also results in some benefits when usedon the lower pressure systems.

For purposes of illustration, the invention is disclosed as applied tomodern steam laundries, its use for other purposes being readilyapparent from the illustrative example. Modern steam laundries generallyemploy the high pressure steam generator which may consist of one ormore generating units connected to a common header from which extends amain steam line connected by branch lines to various types of equipment,such, for example, as tumblers, driers, steam boards, presses, ironers,shell and tube heaters, and the like.

The generator usually has a rated capacity of a predetermined number ofpounds of water per hour evaporated into steam at predeterminedtemperature and pressure. This capacity sometimes is listed as generatorhorse power or B.t.u. capacity, and can be converted readily to thenumber of pounds of water converted to steam at the requisitetemperature and pressure.

Originally, in such systems, the practice was to connect a common steamtrap to the outlets of the various devices for discharging condensatetherefrom. This practice was unsatisfactory and was superseded by thepractice of utilizing separate steam traps, one on each of the steamdevices, and usually one for the header and one for the main steam line.In the case of multiple roll ironers, each roll was considered to be aseparate device, and a separate steam trap was provided for each.

Steam traps are well known and are designed to permit condensate toescape continuously or to accumulate and escape intermittently. Someoperate in response to condensate level and some in response totemperature changes. Others operate electrically. The specific type usedwas unimportant, but whatever type was selected, it was such that, whenopen, it discharged condensate very States Patent rapidly. This wasbecause, since the system was not in balance, as hereinbefore described,a certain amount of wet steam from the generator resulted, and the steamtrap selected was one of a sufii-ciently large output to handle not onlythe normal condensation from the steam devices, but also the carryover.A safety factor was allowed which might vary from one to ten times thenormal condensation rate of the device. It was believed that highefficiency was obtainable only if the condensate from each device weredischarged as rapidly as possible. Thus the selected trap for a givendevice was adequate to discharge condensate therefrom at a much higherrate than the rated capacity of the device.

When these prior systems have been shut down for a period, as in closingdown overnight, the steam generator, the header, the main steam line,and the steam heated devices all cool to an appreciable degree belowoperating temperature. Consequently, a large accumulation of condensatein the system results and a large amount of metal must be brought up totemperature in restoring the system to operation. When heating of asystem in such a condition is initiated, condensate is produced at ahigher rate than in the final operating range. The pressure in thesystem is far below normal. Consequently, the condensate reaches thesteam traps and is discharged into the return line. The steam traps havea capacity of from one to ten times the normal condensate require mentsof the steam devices, because the trap capacities are so great and thetraps are fully open when the pressure starts to rise. Therefore, thesteam being generated begins to flow more rapidly through the pipe linesto the devices, and then through the steam traps, which are still openbecause of condensate and lack of line pressure to close them. In theinitial warm-up stages, as the pressure increases the velocity ofcondensate flow at the discharge side of the steam traps and becomesgreater than the output of the generator. As a result of this velocityincrease, the steam being generated and fed into the steam line is notsufficiently heated, and steam in a wet condition issues from thegenerator and flows throughout the pipe lines and steam devices. Thisstarts a cycle in which the traps discharge both the normal condensationof the devices plus the carryover of wet steam. In so doing, they causethis cycle to continue.

According to the system of the present invention, the discharge of thetraps is limited so that they cannot dis charge at a greater rate thanthe generator is capable of producing. Thus, in the present system, thegenerator is not called upon at any time to produce more than its ratedor actual capacity.

Thus, While the generator is being brought up to operating temperature,it is subjected to an excessive and accumulative burden; first, thelarge accumulated amount of cold condensate being fed into the generatorretards high temperature dry steam generation; second, the large amountof cold piping and number of cold devices being heated up concurrentlycausing exceedingly rapid temperature reduction of such steam is fed tothe line and the formation of more condensate; third, the loss of heatfrom the generated steam to the wet steam and moisture in the systemaggravates the situation; fourth, with traps open widely, the pressurein the system does not build up rapidly and the fiow of steam from thegenerator begins before such steam is at the temperature and pressurerequired; and fifth, the reduced pressure increases the introduction ofwet steam from the generator.

Thus, steam from the generator enters the system while the steam is wetand before it is at the requisite temperature and pressure, oftencarrying over into the system a large amount of suspended droplets ofwater.

The carryover of water, whether as free droplets or as wet steam, lowersthe generator level to such a degree that make-up water must be fed intothe generator to bring the water level up to that required. This againchills the generator and aggravates the condition. This make-up water isa loss in that, should the system become fully operative, too much wateris present. Such excess eventually must be disposed of or separatelyhandled.

As a result of these concurrently existing and cumulafive effects, ifthe operator is not extremely careful in manually controlling each steamdevice as it is being cut-in to the system so that the generator canmaintain a lead in the rate of generation of high pressure dry steamover the rate of condensate formation, the generator can catch up onlyafter a long period of inoperativeness of the system.

The carryover of water from the steam generator into the system has longbeen a problem for which a solution was lacking.

The attempted solution for rectifying such conditions was to see thatthe steam traps had capacities in excess of the rated capacity of thedevices with which they were used, so that the condensate could flowfrom the steam side of the system as rapidly as possible.

This attempted solution overlooked completely that this problem resultedfrom incapacity of the generator to gain on the capacities of the traps.It aggravated the very problem it was meant to solve.

In accordance with the present invention, it has been found that all ofthe devices under such conditions can be connected into the main line inrelatively rapid succession, or concurrently, if the rate of dischargeof the condensate from the various devices is limited so that the totalrate of discharge from the system does not exceed the rated capacity ofthe generator. Thus, by having proper flow control orifices on thedevices, the rate of discharge of condensate from each device is reducedsufiiciently so that the steam from the generator enters the equipmentmore slowly, following up on the very slow regression of the relativelycool accumulated condensate from the system.

This causes the pressure in the main steam line to increase more rapidlyto the temperature and pressure rating of the generator, therebyreducing or preventing carryover of water from the generator. As aresult the output of dry high pressure steam by the generator ever comesthe formation of condensate, forcing it gradually out of the lines anddevices and building up the temperature of all the devices at a rateconsistent with the generator capacity. The rate of escape of condensatefrom each device is independently controllable so that no one device isfreely vented to the return line. Hence no device can initiate watercarryover from the generator.

Specific objects and advantages of the invention will become apparentfrom the following description wherein reference is made to thedrawings, in which:

FIG. 1 is a diagrammatic illustration of the high pressure dry steamsystem employing the principles of the present invention;

FIG. 2 is a diagrammatic illustration of one of the steam operateddevices thereof in the form of a bank of individually controlled units.

Referring to FIG. 1 of the drawings, the system, as embodied in a steamlaundry, comprises a high pressure, steam generator 1 connected to asuitable header 2 from which leads a main steam line 3. A condensatereturn line 4 is provided returning condensate to the steam generator 1.The return condensate is delivered by the line 4 to condensate receivingand return equipment 5 which forces it back into the generator.Likewise, a motor driven pump 6 is provided for pumping, from a suitableexternal source, make up water into a receiver or injector for thegenerator.

The specific steam operated devices used in the system may be varieddepending upon the purposes of the particular installation. For purposesof illustration, a closed system is shown and includes such devices as ashell and tube heater 10, an ironer 11, a tumbler 12, a steam board 13,and a presser 14. The closed steam system is preferred so as to conservethe condensate for re-use. However, if desired, an open system can beused, the steam traps thereof discharging the condensate to an open sumpor drain. The connections and fittings for the devices are the same.

Referring particularly to the heater 10, it is connected by a branchline to the main line 3, a suitable stop cock 16 being interposedbetween the main line 3 and heater 10. The heater 10 has an outlet whichis connected by a discharge line 17 to the inlet of a steam trap 18 ofone of the conventional types. Usually the traps selected are of thetype which open and discharge condensate when a predetermined condensatelevel is reached therein. Other types, such as those which operate onthe basis of the temperature or weight of the condensate may be used.

A suitable stop cock 19 is provided between the line 17 and the inlet ofthe trap 18. A stop cock 20 is provided between the outlet of the trap18 and a branch return line 21. A by-pass line 22, including a stop cock23, is provided in by-passing relation to the stop cocks 19 and 20. Thevarious cocks are arranged for proper servicing of the equipment;

customarily when separate traps are employed, one for each steam device,each trap selected is such that when open to discharge condensate it hasa capacity for discharging the condensate at a rate much greater thanthan required by its associated device.

In accordance with the present invention, the trap 18 is provided with aflow control orifice means which reduces the rate of fiow of condensatefrom the trap so that, while the trap is open, the condensate escapesgradually from its associated device. As hereinbefore mentioned, it isnecessary to reduce the rate of flow so that the total of discharge fromall of the devices in the system does not exceed the horse power orrated capacity of the generator.

While it is possible to incorporate in the body of the trap a flowcontrol orifice means of proper size to reduce the rate of flow to thatrequired, it is to be noted that usually the discharge orifices of thetraps even though adequate to discharge at a rapid rate and much largerthan can be tolerated in the present sytsem', are nonetheless small. Ifof a size for the limiting of the flow as herein contemplated, theywould be so small that would clog easily. Also, if within the trap, theywould be diflicult to service.

Accordingly, orifice means 24 are provided in the discharge line 21between the outlet of the trap 18 and the return line 4.

This orifice means preferably is in the form of a manually adjustableneedle valve of which the elfective orifice size can be adjusted withprecision to assure a maximum rate of fiow considerably below that ofthe trap 18 and a minimum rate of flow adequate to assure discharge ofthe condensate from the trap when the associated device is functioningat its rated capacity. Such an adjustable orifice is preferred as manyfactors enter into the formation of condensate and may vary with theseasons of the year, and compensating adjustment may be required fromtime to time. If this system is not subjected to these changingextraneous conditions, then a fixed orifice, preselected in accordancewith the requirements of the systern, may be employed.

Generally, between the orifice 24 and the return line 4, a check valve25, opening to permit flow of condensate to the return line and closingto prevent the return flow therefrom, is provided.

Furthermore, for purposes of isolating diiferent parts of the equipmentfor service and repair, a stop cock 26 is provided between the checkvalve 25 and the return line 4.

Since the installation and fitting for each device is essentially thesame except for the size of the orifice means, check valve, and stopcocks, the specific installation of each device will not be described indetail, except to note that generally they are connected in parallelacross the steam line and the return line.

The ironer 11 employs a steam trap 30 and an adjustable orifice 31, thetumbler 12, a steam trap 32 and an adjustable orifice 33, the steamboard 13, a trap 34 and an adjustable orifice 35, and the press 14, asteam trap 36 and an adjustable orifice 37.

At this point it is to be noted that the main steam line and the headerare also operating devices, inasmuch as a certain amount of steam isconsumed by them in transmitting it to the other steam consuming devicesand condensate is produced accordingly. The branch lines leading to therecited steam operated devices are usually short and the condensatetherein is considered to be part of the condensate of that specificdevice. Thus, in addition to the devices heretofore recited, the header2 is provided with a trap 40 and an adjustable orifice 41. The mainsteam line 3 is provided with a trap 42 and an adjustable orifice 43.These traps and orifices likewise have the usual stop cocks and checkvalves, arranged as described specifically as those used in connectionwith heater 10.

As illustrated in FIG. 2, the ironer 11 may comprise a plurality ofindividual units or rolls 110, each of which has its individual trap 30awith an adjustable orifice 31a, and check valve and isolating stopcocks. In such case, the operating efiect is the same except that moreaccurate control can be obtained, each roll becoming a separate steamconsuming device. If desired, however, one trap may be used for theironer 11.

Thus, in operation the rated capacity of the generator and of each ofthe various devices being known, traps are chosen as hereinbcforedescribed for the devices, respectively, including one for the mainsteam line 3 and one for the header 2.

Having installed the orifices, and with the system cold, the generatoris started. Each orifice remains fully open to determine whether thesteam generator has the capacity to purge the system of condensate andbring it up to the operating temperature and pressure. Generally, itcannot do so. Each orifice may be reduced in size by operation of theneedle until it becomes apparent that the steam generator can catch upwithin a reasonable time with the formation and discharge of condensate.Watching the gauge of the steam generator and knowing its ratedcapacity, one can determine its rate of approach to its ratedtemperature and pressure output. If losing, each of the orifices isreduced still further until a balance is obtained. If, under suchconditions, any device is not being kept purged of condensate, theorifice therefor can be increased slightly, and one or more of the otherorifices increased if necessary. Necessarily, since the devices,including the steam line and header, do not exceed the rated capacity ofthe generator, a balance is soon reached. Further refinement for optimumefiiciency can be obtained by reducing each orifice still further sothat each has as slow a flow rate as is consistent with the ratedcapacity of its associated equipment. Once the desired balance isobtained, the needle valves may be locked in the final adjusted positionto assure that they will not inadvertently be thrown out of balance inthe future.

With this arrangement, the steam generator can readily bring the systemup to the pressure and temperature which is required in the equipment,and thereafter maintain said pressure and temperature. The main line,header, and the devices are gradually purged without at any timeover-taxing the generator so that the carryover of water from thegenerator is eliminated.

Should it happen that the total of rated capacities of the steam devicesexceeds the capacity of the steam generator, then additional steamgenerating capacity must be added so that the total generator capacityexceeds the total rated capacities of the devices in order for thepresent invention to be fully effective.

Having thus described my invention, I claim:

1. In a steam system:

a steam generator having an output within a predetermined range ofcombined pressure and steam temperature;

a plurality of steam consuming devices connected thereto for receivingsteam therefrom and having a total rated capacity not exceeding therated capacity of the generator;

each of said devices having an outlet;

steam trap means connected to the outlets, respectively, each trap meansbeing capable of discharging all of the condensate of the steam utilizedby its associated device while preventing the escape of steam from itsassociated device;

characterized in that each of said trap means includes flow limitingmeans permitting discharge of condensate up to, but not substantiallyexceeding, the rated capacity of the associated device when the trapmeans are fully open; and

said tlow limiting means of all of the trap means in the system arerelated to the generator so that their combined effect is to restrictthe rate of discharge of condensate from the entire system to a ratesuch that the system remains within the output capacity of the generatorand thereby prevents carryover of wet steam and water from the generatorinto the system.

2. The structure of claim 1 wherein the fiow limiting means of eachdevice has a condensate flow rate capacity substantially equal to therated capacity of the associated device.

3. The structure according to claim 1 wherein said trap means are suchthat, in the absence of their associated flow limiting means, they wouldhave a combined maximum discharge rate greater than the generatorcapacity.

4 The structure according to claim 1 wherein adjustment means areprovided for the flow limiting means, respectively, and are operable toadjust the effective rate of discharge of condensate through theirassociated flow limiting means independently of each other.

5. The structure according to claim 1 wherein the fiow limiting meansfor each trap means is an adjustable needle valve having its inletconnected to the outlet of its associated trap means.

6. The structure according to claim 1 wherein a condensate return lineis provided, discharge lines connect the trap means, respectively, tothe condensate return line, condensate receiving and return equipment isconnected to the return line and to the steam generator and is operableto return the condensate to the generator; and

each of said flow limiting means is connected in the discharge line ofits associated trap means between the outlet of the associated trapmeans and the return line.

7. The structure according to claim 6 wherein manually individuallyadjustable needle valves are provided for the trap means, respectively,each needle valve is disposed in the discharge line of its associatedtrap means, and the flow limiting means of the associated trap means isthe orifice of the associated needle valve.

8. The method of increasing the efiiciency of a steam system whichincludes a steam generator having an output within a predetermined rangeof combined pressure and steam temperature, and a plurality of steamoperated devices connected thereto for receiving steam therefrom, eachof said devices having an outlet;

said method comprising discharging the condensate of the steam utilizedby each device while preventing the escape of steam therefrom, andcontrolling the 7 8 rate of discharge of said condensate from each de-References Cited 3 1 i ifi fiif i iffio i i "i 3322 UNITED STATESPATENTS ensae rorn e n e y ra e suc 1701 143 2/1929 Clarke 122-4 h h t tth the system rernams w1t 1n t e on pu range of 6 3,076,445 2/1963Ohlhaver 122 459 generator and thereby prevents carryover of wet 5 steamand water from the generator into the system. CHARLES J. MYHRE, PrimaryExaminer.

1. IN A STEAM SYSTEM: A STEAM GENERATOR HAVING AN OUTPUT WITHIN APREDETERMINED RANGE OF COMBINED PRESSURE AND STEAM TEMPERATURE; APLURALITY OF STEAM CONSUMING DEVICES CONNECTED THERETO FOR RECEIVINGSTEAM THEREFROM AND HAVING A TOTAL RATED CAPACITY NOT EXCEEDING THERATED CAPACITY OF THE GENERATOR; EACH OF SAID DEVICES HAVING AN OUTLET;STEAM TRAP MEANS CONNECTED TO THE OUTLETS, RESPECTIVELY, EACH TRAP MEANSBEING CAPABLE OF DISCHARGING ALL OF THE CONDENSATE OF THE STEAM UTILIZEDBY ITS ASSOCIATED DEVICE WHILE PREVENTING THE ESCAPE OF STEAM FROM ITSASSOCIATED DEVICE; CHARACTERIZED IN THAT EACH OF SAID TRAP MEANSINCLUDES FLOW LIMITIG MEANS PERMITTING DISCHARGE OF CONDENSATE UP TO,BUT NOT SUBSTANTIALLY EXCEEDING, THE RATED CAPACITY OF THE ASSOCIATEDDEVICE WHEN THE TRAP MEANS ARE FULLY OPEN; AND SAID FLOW LIMITING MEANSOF ALL OF THE TRAP MEANS IN THE SYSTEM ARE RELATED TO THE GENERATOR SOTHAT THEIR COMBINED EFFECT IS TO RESTRICT THE RATE OF DISCHARGE OFCONDENSATE FROM THE ENTIRE SYSTEM TO A RATE SUCH THAT THE SYSTEM REMAINSWITHIN THE OUTPUT CAPACITY OF THE GENERATOR AND THEREBY PREVENTSCARRYOVER OF WET STEAM AND WATER FROM THE GENERATOR INTO THE SYSTEM.